Conventional cell preparation for tests, such as the conventional Pap smear, involve direct application of cellular material to a glass slide which is subsequently processed, screened, and diagnosed by trained professionals. Other methods for preparing cell samples for analysis involve pre-processing of the cell sample prior to application to the slide. Exemplary conventional pre-processing includes vacuum filter deposition onto a slide, electrical charge-based deposition using covalent bonds between the slide and the cells, and manual dilution of the cell sample and manual deposition to the slide. The pre-processing is performed so that when cells are applied to the slide the cells are distributed in a thin layer which allows for a more optimal presentation for diagnostics. In some of these thin-layer methods centrifugation is used to separate cells from other portions (e.g., the supernatant) of the cell sample within a centrifugation tube. Because the cells are heavier than the other portions of the sample, the cells form a pellet in the bottom of the centrifugation tube. The supernatant is then poured off from the centrifuge tube to leave the cell pellet. Samples of the cells within the cell pellet can then be manually prepared on glass slides for analysis by a trained professional.
Manual methods and systems for preparing cell samples on slides rely on visual observation of the cell pellet within the centrifuge tube to make a very crude estimate of the size of the cell pellet. A diluent, such as water, is added to the centrifuge tube to re-suspend the cells, thereby forming a cell suspension. The visual observation of the cell pellet is inconsistent and may not provide an accurate indication of cell pellet size. Consequently, the amount of diluent added based upon this inaccurate and inconsistent observation may also be inconsistent. As a result of human error inherent in a conventional manual method, the cellularity (e.g., the number of cells suspended within the cell suspension) is inconsistent, and thus the prepared sample is inconsistent from one slide to the next.
The actual slide samples are prepared by drawing an amount of the cell suspension from the original centrifuge tube into a pipette. Then an amount of the cell suspension is dispensed by dropping the cell suspension from the pipette from a height above the slide. This procedure is performed by hand and results in inaccuracies and poorly prepared slides.
The inconsistent cellularity of the cell mix coupled with the uncontrolled dispensing results in inconsistent cell samples being placed on the slides for analysis. For example, slides are often prepared with areas that have too many or too few cells per unit area. These areas are often unusable and often render the entire slide unusable for any meaningful analysis. If the slide is unusable, the problem is further complicated if the original sample has been compromised as describe above. This could necessitate a recollection of the sample from the patient.
Accordingly, there exists a need to provide a method and system for thin-layer cell sample slide preparation yielding uniform cell samples through a series of variable dilutions based upon cellularity of the cell sample without compromising the initial cell sample.